The present invention relates to a semiconductor device and a semiconductor electret condenser microphone.
In a portable telephone, an electret condenser microphone which can be easily miniaturized is frequently used. For example, Japanese Patent Publication No. Hei. 11-88992 discloses an example in which a conductive film (hereinafter, referred to as a stationary electrode layer) is formed on an integrated semiconductor substrate, and a vibrating diaphragm is attached onto the stationary electrode layer via a spacer.
FIG. 3 shows the structure of the example. A stationary electrode layer 112, an insulating film 113, a spacer 114, and a vibrating diaphragm 115 are sequentially stacked on the surface of a silicon semiconductor substrate 111. The stacked member is mounted into a package 118 having a through hole 116. The reference numeral 117 denotes cloth which is disposed as required. A junction type FET element for impedance conversion, an amplifying circuit, a noise-canceling circuit, and the like are integrated on the surface of the semiconductor substrate 111 by a usual semiconductor process. In a capacitor formed by the vibrating diaphragm 115 and the stationary electrode layer 112, air vibrations due to a sound cause the vibrating diaphragm 115 to vibrate to change the capacitance, and the capacitance change is input into the FET element to be converted into an electric signal.
In this configuration, in order to enhance the output of the microphone, the capacitance must be increased. It is a matter of course that, preferably, the stationary electrode layer 112 and the vibrating diaphragm 115 are expanded as far as possible so as to increase the overlapping area, and the distance between the stationary electrode layer 112 and the vibrating diaphragm 115 is reduced. In the semiconductor substrate 111, therefore, the stationary electrode layer 112 occupies most area of the substrate, and components to be integrated are placed in the blank area.
When, in order to enhance the output of the microphone, the area of the stationary electrode layer 112 is to be expanded so as to increase the overlapping area between the stationary electrode layer 112 and the vibrating diaphragm 115, however, it is required to increase the size of the semiconductor substrate itself, thereby producing a defect that the production cost is raised.
In order to suppress the production cost, the stationary electrode layer 112 and the vibrating diaphragm 115 may be increased in size while maintaining the current size of the semiconductor substrate. In this case, however, there arises a problem in that the vibrating diaphragm 115 overlaps with terminal pads formed in a periphery of said semiconductor substrate, resulting in a structure in which thin metal wires cannot be connected to the pads.
Referring to FIG. 3, the spacer 114 is placed in the entire surrounding region of the vibrating diaphragm 115, and hence the space defined by the stationary electrode layer 112, the spacer 114, and the vibrating diaphragm 115 is hermetically sealed. Therefore, air cannot enter nor exit from the sealed space, so that the vibrating diaphragm 115 itself hardly vibrates. Even when external sound is transmitted to the vibrating diaphragm, consequently, the vibrating diaphragm vibrates at a small degree, thereby producing a problem in that the output cannot be enhanced.
The invention has been conducted in view of the above-discussed problems. The problems can be solved by a configuration in which a vibrating diaphragm is disposed with protruding a part of the vibrating diaphragm from an end of a semiconductor substrate.
When the vibrating diaphragm protrudes from the periphery of the semiconductor substrate, air vibrations are reflected by the rear face of the protruding vibrating diaphragm, and then easily enter a space defined by the vibrating diaphragm and a stationary electrode layer, with the result that the vibrating diaphragm is allowed to vibrate at a larger degree.
The problems can be solved by a configuration in which a vibrating diaphragm is disposed with protruding a part of the vibrating diaphragm from an end of a semiconductor substrate, and a terminal pad for external connection is exposed, the terminal pad being formed in a periphery of the semiconductor substrate.
The vibrating diaphragm is shifted so as not to overlap with the terminal pad. Even when the vibrating diaphragm protrudes from the semiconductor substrate, therefore, air vibrations are reflected by the rear face of the protruding vibrating diaphragm, and then easily enter a space defined by the vibrating diaphragm and a stationary electrode layer, with the result that the vibrating diaphragm is allowed to vibrate at a larger degree. Since the vibrating diaphragm does not overlap with the terminal pad, moreover, connection of a thin metal wire is enabled.
The problems can be solved by a configuration in which the spacer is discontinuous and is divided.
When the spacer is divided, air can enter and exit from a space defined by the vibrating diaphragm, the spacer, and the stationary electrode layer, through division regions of the spacer. Namely, since air can enter and exit from the space, the vibrating diaphragm can vertically move in an easy manner or vibration is facilitated.
The problems can be solved by a configuration in which an insulating film is formed on a semiconductor wafer, stationary electrode layers are formed on the insulating film in a matrix form,
a spacer configured by an insulating resin film is formed in a periphery of the stationary electrode layers, the semiconductor wafer is then subjected to dicing, thereby forming a semiconductor device, and
a vibrating diaphragm is disposed on the spacer of the semiconductor device.
After the semiconductor wafer is subjected to dicing, the vibrating diaphragm is disposed on the spacer. Therefore, both the shifting and the protrusion of the vibrating diaphragm can be performed.
In a semiconductor electret condenser microphone in which a semiconductor device comprising: a stationary electrode layer which is formed on a surface of a semiconductor substrate; at least two spacers disposed in a periphery of the stationary electrode layer; and a vibrating diaphragm disposed on the spacers is mounted in a hollow package,
a side face of the semiconductor substrate is separated from the package, and a space due to the separation communicates with a space below the vibrating diaphragm via gaps between the spacers. Therefore, the air below the vibrating diaphragm can exit into the space due to the separation, and conversely the air in the space due to the separation can enter the space below the vibrating diaphragm, whereby the vibrating diaphragm is allowed to easily vibrate.